Radiological Protection of the Environment and its Implementation into IAEA Safety Standards
D. Telleria* and G. Proehl
Division of Radiation, Transport and Waste Safety, International Atomic Energy Agency Vienna International Centre, PO. Box 100, A-1400 Vienna, Austria
A R T I C L E I N F O A B S T R A C T Article history:
Received 8 November 2013
Received in revised form 23December 2013 Accepted 30 December 2013
Keywords:
Radiological protection Environment
Reference animals and plants Flora and fauna protection Ecosystems protection
Radiological protection of the environment has been intensively discussed in recent years. Much progress has been made recently with regard to the development of models: (i) to estimate the uptake of radionuclides by flora and fauna in different habitats and ecosystems; (ii) to calculate internal and external exposures for a wide range of terrestrial and aquatic organisms; and (iii) in investigating and analyzing the effects of radiation exposures to biota.
This paper gives an overview of the current status of this work. Furthermore, the current status of the integration of environmental protection into the radiation protection system is also summarized.
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INTRODUCTION
The present article summarize the evolution of the considerations on the radiological protection ot the environment and how the Division of Radiation, Transport and Waste Safety of the International Atomic Energy Agency (IAEA) is incorporating in the initernational safety standards and guidance for radiological protection of people and the environment, the approach developed by the International Commision on Radiation Protection (ICRP) for assessing and control the level of protection of the environment.
The Consideration of protection of the environment from ionizing radiation began in the 1960s and 1970s [1-3], in order to investigate the possible harm to marine flora and fauna arising from the practice of disposing radioactive waste into the oceans. The Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter (London Convention 1972) [3] was an important milestone which stimulated research in this field as well as the development of approaches to take into account impacts of radionuclide substances on non-human species.
For many years the management of environmental releases of radionuclides was based on the evaluation of possible resulting radiation doses to humans. It was considered that the limitation of exposures to humans would also
provide an adequate level of protection to flora
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and fauna living in the same environments [4].
As a result of the pronounced awareness of environmental issues, considerations were initiated with regard to possible radiological impacts to flora and fauna arising from radionuclides released into the environment, irrespectively of their connection with human activities. “Protection of people and the environment - now and in the future” is defined as a key principle of safety in [5] and the ICRP [6]
recommended to demonstrate demonstrate that the environment is appropriately protected against ionizing radiation.
Objectives of radiation protection of the environmental
Whereas the objectives of radiation protection of humans are intended to avoid deterministic effects and to limit stochastic effects to individuals [7], the objectives for the protection of the environment are more complex. The consideration of individual animals or plants is not the aim, but approaches in environmental protection target higher organizational levels such as populations, community levels and ecosystems. The goals are related to the conservation of species, the maintenance of biodiversity and the protection of habitats, communities and ecosystems [6-10]. These goals are rather generic and they are not quantifiable in a straightforward manner. Furthermore, one has to be aware that-in any environment-ionizing radiation may represent only one of many stressors and is very likely not to be the most important one.
In addition, beyond the sole consideration of radiological impact to humans as well as to flora and fauna, radiological protection of the environment has to ensure the sustainability of natural resources, i.e. agriculture, forestry, fisheries and tourism, and of the use of natural resources.
Usually, such considerations are taken into account through the optimization of protection [5,7].
Framework for radiological protection of the environment
With regard to radiological protection of the environment, frameworks have been developed in the context of the EU-funded projects FASSET and ERICA [11,12] and, in parallel, by the ICRP. The approach takes the system for the radiation protection of humans as an example (Fig. 1), it is described in [10,13]. All three exposure situations (i.e. planned, existing and emergency), are considered, as for humans, the assessment of exposures to both humans as well as to flora and fauna are based on measured or estimated radionuclide concentrations in the environment.
In analogy to the reference person [4,6], ICRP defined a number of Reference Animals and Plants (RAPs) [10]. RAPs represent different ecosystems (e.g. terrestrial, freshwater, marine) and different organisms (i.e. animals and plants). The RAPs are described at the taxonomic level of family, if applicable. RAPs have been selected to represent significant wild life groups that are found in most of the environments around the world. Databases have been elaborated in order to enable the estimation of exposures in different natural environments, and the understanding of the significance of the exposure in terms of biological effects [10].
Exposures are calculated for RAPs respectively. Decisions needing to be made in relation to human exposure are guided by
comparison with dose limits and constraints for planned exposures and with reference levels for existing and emergency exposure
situations. Exposures to biota may be evaluated by comparison with reference criteria like the Derived Consideration Reference Levels
(DCRLs), as defined by ICRP [10], taking into account the specific conditions of the exposure situations [13].
SCIENTIFIC BACKGROUND
Much work was done during the last decade
to elaborate the basis for the assessment and evaluation of radiological impacts to flora
and fauna. in 2005, the ICRP established a Committee dedicated to Protection of the Environment with the aim of setting up a framework for assessment and evaluation of exposures to biota.
The work of the Committee was closely linked to the activities of the EU-funded projects FASSET and ERICA [11,12].
Planned, existing, and emergency situations
Environmental concentrations
Reference Animals and Plants
Dose limits Dose constraints Reference levels
Decision making
Derived Consideration Reference Levels Reference Persons
Humans Biota
Fig. 1. Scheme for estimating and evaluating exposures to humans and biota.
Table 1. Reference Animals and Plants as derived in [10].
Ecosystem Wildlife group Reference Terrestrial Large terrestrial
mammal
Reference deer
Small terrestrial mammal
Reference rat
Large terrestrial plant
Reference pine
Small terrestrial plant
Reference grass
Insect Reference bee
Annelid Reference
earthworm Terrestrial/aquatic Amphibians Reference frog
Aquatic bird Reference duck Freshwater Freshwater pelagic
fish
Reference trout
Marine Seaweed Reference brown
seaweed Marine
crustaceans
Reference crab
Marine fish Reference flatfish (benthic)
The approach to assess exposures is summarized in Fig. 2. Following the releases of radionuclides to the aquatic or terrestrial environments, flora and fauna may receive radiation
doses through internal and external exposure.
The assessment of exposures starts from measured or estimated activity concentrations in water, sediments or soil. For their estimation, the same dispersion models typically used for the estimation of doses to members of the public arising from discharges to the environment can be applied.
Specific data needed for the exposures of reference animals and plants are: (1) Transfer parameters are compiled to allow the estimation of the uptake by reference animals and plants from water, sediments or soil in order to calculate activity concentrations in reference animals and plants [14].
A compilation of transfer parameters for a wider range of taxa is published in [15]. The values provide the ratio of the average activity concentration in the considered reference organism and the surrounding environmental medium; and (2) Dose conversion coefficients (DCC) for assessing internal and external radiation exposures to terrestrial and aquatic biota were developed.
The DCCs for internal exposure are calculated for a homogeneous distribution of the radionuclides in both terrestrial and aquatic organisms. For the calculation of DCCs for external exposure, it is assumed that aquatic organisms are immersed by water; for terrestrial RAPs, habitats in-soil, on-soil and above-soil are assumed.
Based on an analysis of the existing data on radiation effects in cells, tissues, organisms and - in a few cases - on population and ecosystems, the ICRP has derived the set of Derived Consideration Reference Levels (DCRL) for the 12 RAPs. These DCRLs, which are bands of doses which cover one order of magnitude (Table 2), represent bands of doses that are associated with no, or very little, adverse effects. A wide range of effects has been considered and are classified into rbidity, mortality, reduced success in reproduction and mutations.
DCRLs do not represent dose limits, they should be considered as zones of doses at which a more detailed analysis should be carried out. For this evaluation of the exposure conditions, factors
should be taken into account such as, e.g. the type of exposure situation (i.e. planned, existing,
emergency), the size of area that is affected, the time period for such exposures, the fraction of a population of a species that is exposed to such dose levels, the appropriateness of the database used for the dose estimation, and the degree of precaution that is needed for the assessment.
Discharges to the environment
Aquatic environment Terrestrial environment
Water Sediments
Total (internal and external) exposure
Activity in soil
Total (internal and external) exposure
Uptake Uptake
Internal
Dosimetry External
Dosimetry Internal
Dosimetry External Dosimetry
Evaluation of exposures to biota Derived Consideration Reference Levels
(12 Reference Animals and Plants)
TRANSFER AND DOSIMETRYEFFECTS
Fig. 2. Scheme to estimate and evaluate exposures to biota in the aquatic and terrestrial environments.
Table 2. Derived Consideration Reference Levels for Reference Animals and Plants [10].
Reference Animal and Plants Derived Consideration Reference Level (mGy/d) Reference deer, rat, duck, pine 0.1-1
Reference frog, trout, flatfish,
brown seaweed, grass 1-10
Reference bee, earthworm,
crab 10-100
RESULTS AND DISCUSSION
Implementation of radiological protection of the environment in the IAEA basic safety standards and related safety guides
In the IAEA’s International Basic Safety Standards [7], objectives for radiological protection of flora and fauna are defined in accordance with [6]
(section 2). However, it is also stressed that radiological protection of the environment should not be considered in isolation since man is an integral part of the environment. Besides the pure radiological protection of man and flora and fauna, the sustainable use of natural resources for e.g.
agriculture, forestry fishery and tourism – now and in the future – should be ensured, which is in
general warranted by the appropriate application of the optimization principle [5]. The BSS [7]
explicitly requires the consideration of protection of the environment for registration and licensing of activities during setting discharge limits for facilities, it is not specified to what level of detail this should be considered. Specific numerical dose
levels to be applied for control of exposures of flora and fauna are not included in the BSS.
Protection of the environment is one factor for consideration during optimization in existing and emergency exposure situations.
Four IAEA Safety Guides are currently being revised or newly developed in order to address requirements of the BSS with regard to exposures of the public and the consideration of radiological impacts to the environment from radionuclides released to, or existing in, the environment. Planned, existing and emergency exposure situations are addressed; the recommendations are summarized in the following key points: (1) For planned exposure situations, e.g. when setting conditions for radionuclide discharges to the terrestrial or aquatic environments, the lower boundary of the relevant DCRL band (Table 2) should be applied as a reference for protection of different types of biota within a given area. The impact of multiple sources should be taken into account. Should resulting exposures to the different types of biota exceed the lower end of the DCRL, further actions to improve the level of protection could be considered, bearing in mind that DCRLs are not limits and taking into account the specific circumstances of exposures. If doses to the considered biota are above the upper end, the planned activity would very likely create a significant environmental contamination, indicates a stronger need for further protection efforts. The potential environmental consequences of emergency actions should be considered as part of the planning phase, which will in turn involve consideration and optimization of protection strategies; and (2) For existing and emergency exposure situations, radiological impacts to wildlife cannot, or only marginally, be controlled. However, the environmental consequences of the mitigating and remediation actions for optimizing human protection should be taken into account, as appropriate. The set of the DCRL’s might be used for providing information of the radiological impacts and possible effects to wildlife and how long such effects are going to exist.
CONCLUSION
Radiological protection of the environment is a topic that has been intensively discussed in the recent years. The main achievements are summarized below.
Frameworks have been developed to estimate the exposures of reference animals and plants, flora and fauna and to evaluate exposures with regard to adverse effects induced by ionizing radiation. These methods allow the assessment of external and
internal exposures to RAPs in terrestrial and aquatic environments.
For the evaluation of exposures, the ICRP has derived DCRLs, a set of bands of dose rates for the RAPs within which there is likely to be some chance of deleterious effects of ionizing radiation occurring to individuals of that type of reference animal or plant.
The consideration of the protection of the environment has been included in the International Basic Safety Standards and guidance is currently being developed for the implementation of these requirements.
It should be noted that routine discharges of radionuclides to the environment that comply with radiation protection criteria for humans may hardly affect wildlife, whereas exposures to wildlife in the band of the Derived Consideration Reference Levels would very likely imply restrictions with regard to human activities in those areas.
As environmental protection issues attract public attention, further scientific studies would improve the understanding of the interaction of ionizing radiation on communities, habitats and ecosystems and facilitate the communication with the public. This is in particular important for the analysis and evaluation of effects that might be reported for areas affected by nuclear accidents.
Exposures to humans and to wildlife should not be considered in isolation, but assessed and evaluated in an integrated approach in order to achieve consistent conclusions and well-balanced decisions.
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